Many battery powered devices, such as cell phones, tablets, ebook readers, and the like, have one or more intermediated active states and a sleep (or hibernate) state for conserving battery power. The sleep state typically draws significantly less current than the active states. For example, a cell phone may draw about 500 uA while powered down in a sleep state and about 2 A while transmitting in a communication state. Designers of such battery powered devices generally attempt to maximize battery life. In order to accurately test designs, the different currents must be measured while the battery powered devices operate in the various different states. However, displays of conventional oscilloscopes have resolution limitations that prevent useful, simultaneous display of small current portions of the signals in the sleep state and large current portions of the signals in the communication state.
For example, a cell phone may have three states: a sleep state (low power state) in which the cell phone is not being actively used, but is still powered on and ready to receive calls or data in response to wake-up commands; a chores state (intermediate power state) in which the cell phone is performing housekeeping functions, such as checking for appointments, refreshing statuses of applications, checking battery level and receiving status updates from hardware, but is not actively transmitting or receiving calls; and a communication state (high power state) in which the cell phone is actively transmitting or receiving, such as transmitting or receiving calls or “checking in” with base stations to provide status or location information. Typically, such a cell phone draws current on the order of microamps (e.g., 500 μA) in the sleep state, on the order of milliamps (e.g., 1 mA) in the chores state, and on the order of amps (e.g., 2 A) in the communication state. Due to the large differences in current among the various states and resolution limitations of an oscilloscope display, the current signals cannot be displayed and/or measured using the same oscilloscope display. For example, if peak current indicated by a large current portion of the signal waveform (e.g., in the communication state) observed from the cell phone is 2 A, and the oscilloscope is set to the optimum setting for the channel providing the large current portion of the signal, the displayed signal waveform will fill the display screen. Assuming the oscilloscope has eight bits of resolution, the minimum level that may be observed on the oscilloscope display is greater than 8 mA (i.e., 2 A/28=8 mA). Therefore, a small current portion of the signal waveform (e.g., in the sleep state) will be in the noise on the displayed signal waveform.